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Sickle Cell Anemia

Sandra L Mondro, MD
J Stevan Nagel, MD

January 31, 1995

Presentation

A 19-year-old woman with sickle cell anemia presents with a two day crisis consisting of fever, joint pain, and left upper quadrant discomfort.

Imaging Technique

Delayed planar scintigraphy with intravenous injection of 25 mCi of technetium-99m methylene diphosphonate (MDP).

Imaging Findings

Radionuclide scintigraphy

Radionuclide scintigraphy shows abnormal tracer uptake in the spleen (arrow). There is mild prominence of tracer accumulation within both kidneys (arrows), which appear slightly enlarged. There is abnormal tracer accumulation adjacent to several major joints, including both sides of the knees (arrows) and in the humeral heads bilaterally (arrows).

Differential Diagnosis

Splenic uptake of Tc 99m MDP is abnormal; this can be seen with infarction, usually with a history of sickle cell disease. Other etiologies include glucose-6-phosphate dehydrogenase deficiency, thalassemia major, or hemosiderosis. Tracer uptake within microcalcifications secondary to these diseases or any other cause of dystrophic calcification deposition can lead to splenic visualization. A prior recent liver-spleen scan (Tc 99m sulfur colloid) or other radionuclide that normally demonstrates splenic uptake may be considered.

Normal bone scintigraphy exhibits mild normal kidney uptake. However, renal tracer accumulation greater than lumbar spine uptake is abnormal. Any condition producing excess tissue calcium (such as sickle cell disease, hyperparathyroidism, hypercalcemia from many causes, tissue damage secondary to chemotherapy, radiation, antibiotics such as amphotericin B or aminoglycosides, acute tubular necrosis, or multiple myeloma) could be considered. Dehydration also can cause abnormal bilateral uptake. Any state leading to systemic iron overload can cause renal failure and subsequent increased uptake, but depends on the stage of the disease process.

Diffuse periarticular uptake can be seen with infection, bone infarction, and marrow hyperplasia, as seen with chronic anemia.

Discussion

The primary pathophysiology of sickle cell disease is related to the unusual properties of the damaged, sickling red blood cells. Excluding the hematologic system, the skeleton is the most common site to lead to clinical symptoms. The majority of painful crises are initiated by bony microvascular occlusion, leading to ischemia of the juxtaarticular bone marrow. Acute long bone infarcts primarily occur in children less than ten years of age, and most commonly involve the metadiaphyseal regions.

Abnormal tracer accumulation secondary to osteomyelitis may be difficult to distinguish from infarction on bone scan. Sickle cell disease carries an increased incidence of bone infection, most commonly from staphylococcus or salmonella. On bone scintigraphy, infarcts usually show an area of diminished tracer uptake 7 to 10 days post event. Osteomyelitis characteristically leads to increased tracer uptake during this period. Discrepancies have been reported with these patterns; In 111 tagged white blood cells and Ga 67 citrate have been conjuctively used to increase detection sensitivity for infection. Both of these concentrate in infected bone earlier than Tc 99m MDP. A disadvantage with these agents is the need for delayed imaging (6 to 48 hours).

In young patients with sickle cell disease, the kidneys are usually enlarged. They become small and scarred over time secondary to progressive renal failure. These patients are prone to acute pyelonephritis. Therefore, urinalysis may prove helpful in detection of infarction since the kidneys will show abnormal accumulation in the presence of infection.

Splenic enlargement occurs early with sickle cell disease, but rarely persists into late childhood. Repeated microinfarctions lead to loss of function, eventual fibrosis and calcification (autosplenectomy).

References

1. Palmer EL. Practical nuclear medicine. WB Saunders, 1992.

2. Macperson RI, et al. Sickle cell anemia: an old disease with new imaging. Postgrad Radiol, 1994;14(4).

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